The ability to form a layer of multiconstituent material on a substrate of different composition, especially the ability to form a multiconstituent epitaxial layer (referred to as a heteroepitaxial layer), is of current or potential importance in many fields of technology, e.g., in semiconductor device manufacture or integrated optics.
In particular, heteroepitaxy has been a field of active research for some time. These efforts have led to some technologically important applications. For instance, the III-V or II-VI semiconductors have been combined with ternary materials in heteroepitaxial systems. Exemplary of this application is GaAs/Al.sub.x Ga.sub.1-x As that is widely used in opto-electronic devices. Patterned monocrystalline layers of III-V compounds have also been grown on III-V substrates (U.S. Pat. No. 3,928,092, issued Dec. 23, 1975 to W. C. Ballamy et al). Semiconductor layers are also being grown epitaxially on insulators. An example of such a heteroepitaxial system of technological importance is silicon on sapphire. Similarly, compound semiconductors, especially the III-V compounds, have been grown on sapphire substrates. For a general review, see for instance, Heteroepitaxial Semiconductors for Electronic Devices, G. W. Cullen and C. C. Wang, editors, Springer-Verlag, New York (1978).
Despite the efforts of the last years, the number of heteroepitaxial systems that have been developed sufficiently to permit electronic device application is small. In particular, the number of demonstrated structures comprising an epitaxial metal layer and/or an epitaxial insulator on a semiconductor substrate is at present very limited. However, such systems not only are required for three-dimensional integrated circuits, but would permit the realization of novel device structures, e.g., a metal base transistor. Chief among the reported heterostructures containing an epitaxial metal layer are CoSi.sub.2 on Si, and NiSi.sub.2 on Si.
Prior art methods for forming metal silicides on Si(111) typically involve depositing the silicide-forming metal onto the silicon substrate, followed by heating the substrate, thereby forming a sequence of increasingly Si-rich silicides, (e.g., Ni.sub.2 Si.fwdarw.NiSi.fwdarw.NiSi.sub.2). The resulting epitaxial silicide layers, however, typically are not single crystal. Instead, the epitaxial material formed typically consists of two types of crystallites, both sharing the surface normal [111] direction with the substrate, but one having an orientation that is rotated by 180 degrees about the normal, as compared to the substrate ("type B"), and the other having an orientation that is identical to that of the substrate ("type A"). These crystallites of course are separated by high-angle grain boundaries which reduce the usefulness of this material as conductor material in VLSI semiconductor devices. Furthermore, the presence of both A and B type crystallites typically makes such material unsuitable as substrate layer for the growth of device-quality heteroepitaxial material thereon, e.g., growth of a further Si layer, as would be required in the manufacture of three-dimensional integrated circuits.
These prior art methods have also been unsuccessful in growing single crystal NiSi.sub.2 on Si(100), due to (111) faceting of the NiSi.sub.2 /Si interface. See for instance K. C. Chiu et al, Applied Physics Letters, Vol. 38, pp. 988-990 (1981). Growth of metal silicide with a uniform interface on Si(100) is, however, of great technological importance since current silicon technology uses almost exclusively (100)-oriented material. For the same reason, the growth of epitaxial single crystal metal silicides on Si(100) is important.
A method for forming single crystal metal silicide-silicon heterostructures was disclosed, together with devices based on such a structure, in commonly assigned U.S. Pat. No. 4,492,971, issued Jan. 8, 1985, to J. C. Bean et al, entitled, "Metal Silicide-Silicon Heterostructures". See also commonly assigned U.S. Patent Application Ser. No. 445,014, filed Nov. 29, 1982, a division of U.S. Pat. No. 4,492,971. The above application teaches that essentially monocrystalline silicide can be grown epitaxially on a single crystal silicon substrate by exposing the substrate to a vapor comprising a silicide-forming metal, e.g., to Ni vapor, while heating the substrate to a temperature in the range of 550 to 850 degrees C. Under these conditions, the metal reacts in situ as it deposits and forms a layer of epitaxial single crystal silicide, e.g., NiSi.sub.2.
A method for forming a single crystal heteroepitaxial layer of multiconstituent material on a substrate that can, inter alia, be advantageously applied to the growth of epitaxial metal silicide layers on silicon, including NiSi.sub.2 on Si(100), was disclosed by J. M. Gibson et al, in commonly assigned U.S. Pat. No. 4,477,308, issued Oct. 16, 1984, entitled, "Heteroepitaxy of Multiconstituent Material by Means of a Template Layer". The application teaches that single crystal multiconstituent epitaxial layers, e.g., NiSi.sub.2, can be grown on an appropriate single crystal substrate by depositing a thin disordered layer of "template-forming" material, e.g., Ni, on the substrate surface at a relatively low deposition temmperature, raising the substrate temperature to an intermediate transformation temperature, thereby causing the template-forming material to undergo a solid state reaction that results in formation of "template" material, e.g., substantially NiSi.sub.2. Onto the thus formed thin template layer is then deposited the material for the multiconstituent layer, e.g., Ni, or Ni and Si, with the substrate maintained at a (typically higher) temperature at which the equilibrium silicide, e.g., NiSi.sub.2, is formed by a solid state process.
Surface alloying by irradiation-induced melting has also been used to form metal silicides on silicon. For instance, J. M. Poate et al, Applied Physics Letters, Vol. 33, pp. 918-920, (1978) report alloying Pt, Pd, and Ni films to Si using Q-switched Nd-YAG radiation. Irradiating the metal film, deposited onto a Si Substrate, with such radiation, of intensity sufficient to produce melting of the metal, resulted in macroscopically very uniform alloy layers whose average composition could be changed over a wide range by varying film thickness and/or laser power. The reacted layer, however, consisted not of single phase material but had a cellular microstructure, with typical cell diameters of 1000 .ANG..
T. W. Sigmon reports (pp. 511-523 l of Laser and Electron-Beam Solid Interactions and Materials Processing, J. F. Gibbons et al, editors, MRS Symposia Proceedings, Vol. 1, (1981), North Holland, N.Y.) that single phase silicides can be formed by heating a metal layer on Si in the solid state with CW lasers. Again, the resulting silicide is not single crystal material, and thus typically not acceptable for many possible device applications.
Because of the technological importance of structures comprising a multiconstituent material layer on a substrate, especially of an epitaxial metallic, semiconducting, or insulating layer on silicon or other semiconductor substrate, and of uniform interfaces in Si(100) heterostructures, methods for producing such structures are of considerable interest. Of special interest would be a method for producing such structures that can be practiced without the use of ultra-high vacuum conditions. This application discloses such a method.